Bettencourt has acknowledged the existence of the Swiss accounts and said she will repatriate the $100m held in them and settle up with the tax authorities.
She was also questioned about allegations by a former bookkeeper that she and her late husband made large illegal cash payments to conservative politicians.
These were alleged to include donations to Eric Woerth, the country's labour minister, to fund the 2007 election campaign of Nicolas Sarkozy, the French president.
"On the financing of political parties, she confirmed that this had never been her centre of interest and that it was more her husband's field when he was alive," Kiejman said.
Bettencourt was questioned on Monday in her villa in the wealthy Paris suburb of Neuilly.
By contrast, others protagonists in the affair have been summoned to the headquarters of the Paris financial crimes division and some held overnight in police custody.
Woerth's wife, Florence, worked for Bettencourt's wealth manager while Woerth was budget minister in charge of tax affairs and treasurer of the ruling UMP party.
The minister has denied receiving any illegal money from Bettencourt and has rejected accusations of a conflict of interest.
Bettencourt told police she vaguely remembered having had dinner with Woerth once but did not recall his wife, who was not one of her close staff, according to her lawyer.
Woerth is expected to be questioned by police later this week after the cabinet gave permission last Wednesday.
He has refused to resign and says he will continue to lead a major pension reform due to be adopted by parliament in October.
Bettencourt, 87, inherited L'Oreal from her father, the company's founder, and has an estimated fortune of $20bn.